Turbine airfoil trailing edge cooling slot

ABSTRACT

A turbine airfoil includes pressure and suction sidewalls extending along a span from a base to a tip. Spanwise spaced apart trailing edge cooling holes in pressure sidewall end at a trailing edge cooling slot extending chordally substantially to an airfoil trailing edge. Each cooling hole includes a curved inlet, a metering section with a constant area and constant width flow cross section, and a spanwise diverging section leading into slot. Axial partitions extend chordally between and radially separate cooling holes along span. Aft ends of partitions include swept boat tails. Upper and lower deck sidewalls spanwise bound a deck of slot and extend outward to an external surface of pressure sidewall. Fillets between sidewalls and deck have fillet radii substantially the same size as bottom corner radii of flow cross section of diverging sections adjacent bottom corner radii.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to gas turbine engine turbine airfoil cooling and, more specifically, to turbine airfoil trailing edge cooling slots.

2. Description of Related Art

In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases. The hot gases are channeled through various stages of a turbine which extract energy therefrom for powering the compressor and producing work, such as powering an upstream fan in a typical aircraft turbofan engine application.

The turbine stages include stationary turbine nozzles having a row of hollow vanes which channel the combustion gases into a corresponding row of rotor blades extending radially outwardly from a supporting rotor disk. The vanes and blades have corresponding hollow airfoils with corresponding cooling circuits therein.

The cooling air is typically compressor discharge air which is diverted from the combustion process and, therefore, decreases overall efficiency of the engine. The amount of cooling air must be minimized for maximizing the efficiency of the engine, but sufficient cooling air must nevertheless be used for adequately cooling the turbine airfoils for maximizing their useful life during operation. Each airfoil includes a generally concave pressure sidewall and, an opposite, generally convex suction sidewall extending longitudinally or radially outwardly along a span from an airfoil base to an airfoil tip and axially in a chordwise direction between leading and trailing edges. For a turbine blade, the airfoil span extends from a root at the radially inner platform to a radially outer tip spaced from a surrounding turbine shroud. For a turbine vane, the airfoil extends from a root integral with a radially inner band to a radially outer tip integral with an outer band.

Each turbine airfoil also initially increases in thickness aft of the leading edge and then decreases in thickness to a relatively thin or sharp trailing edge where the pressure and suction sidewalls join together. The wider portion of the airfoil has sufficient internal space for accommodating various forms of internal cooling circuits and turbulators for enhancing heat transfer cooling inside the airfoil, whereas, the relatively thin trailing edge has correspondingly limited internal cooling space.

Each airfoil typically includes various rows of film cooling holes extending through the sidewalls thereof which discharge the spent cooling air from the internal circuits. The film cooling holes are typically inclined in the aft direction toward the trailing edge and create a thin film of cooling air over the external surface of the airfoil that provides a thermally insulating air blanket for additional protection against the hot combustion gases which flow over the airfoil surfaces during operation.

The thin trailing edge is typically protected by a row of trailing edge cooling slots or a single elongated slot which breach the pressure sidewall at a breakout immediately upstream of the trailing edge for discharging film cooling air thereover. Each trailing edge cooling slot has an outlet aperture in the pressure side which begins at a breakout and may or may not be bounded in the radial direction by exposed lands at aft ends of axially extending partitions which define the cooling slots.

The axial partitions may be integrally formed with the pressure and suction sides of the airfoil and themselves must be cooled by the air discharged through the cooling slots defined thereby. The partitions typically converge in the aft direction toward the trailing edge so that the cooling slots diverge toward the trailing edge with a shallow divergence angle that promotes diffusion of the discharged cooling air with little, if any, flow separation along the sides of the partitions.

Aerodynamic and cooling performance of the trailing edge cooling slots is directly related to the specific configuration of the cooling slots and the intervening partitions. The flow area of the cooling slots regulates the flow of cooling air discharged through the cooling slots and the geometry of the cooling slots affects cooling performance thereof.

The divergence or diffusion angle of the cooling slots can effect undesirable flow separation of the discharged cooling air which would degrade performance and cooling effectiveness of the discharged air. This also increases losses that negatively impact turbine efficiency. Portions of the thin trailing edge directly under the individual cooling slots are effectively cooled by the discharged cooling air, with the discharged air also being distributed over the intervening exposed lands at the aft end of the partitions. The lands are solid portions of the pressure sidewall integrally formed with the suction sidewall and must rely for cooling on the air discharged from the adjacent trailing edge cooling slots.

Notwithstanding, the small size of the these outlet lands and the substantial cooling performance of the trailing edge cooling slots, the thin trailing edges of turbine airfoils nevertheless, typically, limit the life of those airfoils due to the high operating temperature thereof in the hostile environment of a gas turbine engine.

Accordingly, it is desired to provide a turbine airfoil having improved trailing edge cooling and cooling slots for improving airfoil durability and engine performance. It is also desired to minimize the amount of cooling flow used for trailing edge cooling in order to maximize fuel efficiency of the turbine and the engine.

SUMMARY OF THE INVENTION

A gas turbine engine turbine airfoil includes widthwise spaced apart pressure and suction sidewalls extending outwardly along a span from an airfoil base to an airfoil tip and extending in a chordwise direction between opposite leading and trailing edges. A spanwise row of spanwise spaced apart trailing edge cooling holes encased in the airfoil between the pressure and suction sidewalls end at a single spanwise extending trailing edge cooling slot extending chordally substantially to the trailing edge. Each of the cooling holes includes in downstream serial cooling flow relationship, a curved inlet, a metering section with a constant area and constant width flow cross section, and a spanwise diverging section leading into the trailing edge cooling slot. Axial partitions extend chordally between and radially separate the cooling holes along the span. Aft ends of the partitions include swept boat tails.

The boat tails may be swept with each of the boat tails including a boat tail trailing edge having an apex spanwise located between the pressure and suction sidewalls. The boat tail trailing edge sweeps aftwardly or downstream from the apex. The boat tail trailing edge sweeps from the apex spanwise or radially outwardly to the pressure sidewall and inwardly to the suction sidewall from the apex. The swept boat tails may further include rounded cross sections through the aft ends of the partitions between spanwise pairs of adjacent cooling holes.

The pressure and suction sidewalls may include pressure and suction sidewall surfaces respectively in the hole and the pressure sidewall surface may be planar through the entire metering and diverging sections. The width may be constant through the metering and diverging sections of the hole.

The airfoil may include a deck in the slot extending chordwise or downstream from the diverging sections of the cooling holes substantially to the airfoil trailing edge and extending spanwise or radially outwardly from a bottommost one to a topmost one of the trailing edge cooling holes. Upper and lower deck sidewalls spanwise bound the deck and extend from the deck to an external surface of the pressure sidewall. Fillets in slot corners between the upper and lower deck sidewalls and the deck have fillet radii substantially the same size as bottom corner radii of the flow cross section of the diverging sections adjacent the bottom corner radii.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and other features of the invention are explained in the following description, taken in connection with the accompanying drawings where:

FIG. 1 is a longitudinal, sectional view illustration of an exemplary embodiment of turbine vane and rotor blade airfoils having cooling holes culminating at a spanwise extending trailing edge cooling slot.

FIG. 2 is an enlarged view illustration of a blade illustrated in FIG. 1.

FIG. 3 is a pressure side sectional view illustration of the cooling holes with constant width metering and diffusing sections leading into the trailing edge cooling slot illustrated in FIG. 2.

FIG. 4 is a cross sectional schematical view illustration of the cooling holes with constant width metering and diffusing sections leading into the trailing edge cooling slot taken through 4-4 in FIG. 3.

FIG. 5 is an upstream looking perspective view illustration of the cooling holes and the trailing edge cooling slot illustrated in FIG. 3.

FIG. 6 is an enlarged perspective view illustration of boat tail aft ends of axial partitions between the cooling holes illustrated in FIG. 5.

FIG. 7 is a cross sectional schematical view illustration of an elongated flow cross section in the constant width metering section taken through 7-7 in FIG. 3.

FIG. 8 is a cross sectional schematical view illustration of an elongated flow cross section in the diffusing section taken through 8-8 in FIG. 3.

FIG. 9 is a cross sectional schematical view of a race track shaped flow cross section having four equal radii.

FIG. 10 is a cross sectional schematical view of an alternative race track shaped flow cross section with a larger width to height ratio than the race track shaped flow cross section illustrated in FIG. 9.

FIG. 11 is a cross sectional schematical view of an alternative flow cross section with unequal top and bottom corner radii.

FIG. 12 is a cross sectional schematical view of another alternative flow cross section with in elongated and fully curved and includes curved quarter sides.

DETAILED DESCRIPTION OF THE INVENTION

Illustrated in FIG. 1 is an exemplary gas turbine engine high pressure turbine stage 10 circumscribed about an engine centerline axis 8 and positioned between a combustor 20 and a low pressure turbine (LPT) 24. The combustor 20 mixes fuel with pressurized air for generating hot combustion gases 19 which flows downstream D through the turbines.

The high pressure turbine stage 10 includes a turbine nozzle 28 upstream of a high pressure turbine (HPT) 22 through which the hot combustion gases 19 are discharged into from the combustor 20. The exemplary embodiment of the high pressure turbine 22 illustrated herein includes at least one row of circumferentially spaced apart high pressure turbine blades 32. Each of the turbine blades 32 includes a turbine airfoil 12 integrally formed with a platform 14 and an axial entry dovetail 16 used to mount the turbine blade on a perimeter of a supporting rotor disk 17.

Referring to FIG. 2, the airfoil 12 extends radially outwardly along a span S from an airfoil base 34 on the blade platform 14 to an airfoil tip 36. During operation, the hot combustion gases 19 are generated in the engine and flow downstream D over the turbine airfoil 12 which extracts energy therefrom for rotating the disk supporting the blade for powering the compressor (not shown). A portion of pressurized air 18 is suitably cooled and directed to the blade for cooling thereof during operation.

The airfoil 12 includes widthwise spaced apart generally concave pressure and convex suction sidewalls 42, 44. The pressure and suction sidewalls 42, 44 extend longitudinally or radially outwardly along the span S from the airfoil base 34 to the airfoil tip 36. The sidewalls also extend axially in a chordwise direction C between opposite airfoil leading and trailing edges LE, TE. The airfoil 12 is hollow with the pressure and suction sidewalls 42, 44 being spaced widthwise or laterally apart between the airfoil leading and trailing edges LE, TE to define an internal cooling cavity or circuit 54 therein for circulating pressurized cooling air or coolant flow 52 during operation. The pressurized cooling air or coolant flow 52 is from the portion of pressurized air 18 diverted from the compressor.

The turbine airfoil 12 increases in width W or widthwise from the airfoil leading edge LE to a maximum width aft therefrom and then converges to a relatively thin or sharp airfoil trailing edge TE. The size of the internal cooling circuit 54 therefore varies with the width W of the airfoil, and is relatively thin immediately forward of the trailing edge TE where the two sidewalls integrally join together and form a thin trailing edge portion 56 of the airfoil 12. A spanwise extending trailing edge cooling slot 66 is provided at or near this thin trailing edge portion 56 of the airfoil 12 to cool it.

Referring to FIGS. 3 and 5, a spanwise row 38 of spanwise spaced apart trailing edge cooling holes 30 encased or buried and formed in the airfoil 12 between the pressure and suction sidewalls 42, 44 end at the trailing edge cooling slot 66. The trailing edge cooling slot 66 extends chordally substantially to the trailing edge TE. The trailing edge cooling holes 30 are disposed along the span S of the trailing edge TE in flow communication with the internal cooling circuit 54 for discharging the coolant flow 52 therefrom during operation. A floor or deck 130 of the slot 66 extends chordwise or downstream from the diverging sections 102 of the cooling holes 30 substantially to the airfoil trailing edge TE. The deck 130 extends spanwise or radially outwardly from a bottommost one 132 to a topmost one 134 of the trailing edge cooling holes 30. The deck 130 is spanwise bound by upper and lower deck sidewalls 136, 138 which extend from the deck 130 to an external surface 43 of the pressure sidewall 42. A slot surface 60 extends widthwise between the upper and lower deck sidewalls 136, 138 along the deck 130. Fillets 62 in slot corners 64 between the upper and lower deck sidewalls 136, 138 and the deck 130 have fillet radii RF that may be substantially the same size as bottom corner radii RT of the flow cross section 74 of the diverging sections 102 adjacent the bottom corner radii RT (illustrated in FIGS. 7-10). The fillet radii RF helps with castability of the trailing edge cooling slot 66.

The trailing edge cooling holes 30 are illustrated in more particularity in FIG. 3. Each cooling hole 30 includes, in downstream serial cooling flow relationship, a downstream converging or bellmouth shaped curved inlet 70, a constant area and constant width flow cross section metering section 100, and a spanwise diverging section 102 which leads into the trailing edge cooling slot 66 and supplies the slot with cooling air or coolant flow 52. Referring to FIGS. 4-6, the trailing edge cooling slot 66 begins at a breakout 58 located at downstream ends 69 of the diverging sections 102. The diverging sections 102 of the cooling holes 30 lead into the trailing edge cooling slot 66 which breaches the external surface 43 of the pressure sidewall 42 at a breakout lip 49 spaced forward or upstream from the trailing edge TE.

Referring to FIGS. 3 and 5, the cooling holes 30 are separated radially along the span S from each other by corresponding axial partitions 68 which extend downstream toward the trailing edge TE. The curved inlet 70 is illustrated herein as downstream converging or, more particularly, a bellmouth inlet. The inlet 70 is defined at and between forward ends 72 of the partitions 68. The partitions 68 include semi-circular forward ends 72 having diameters 73 that define the bellmouth inlet 70. Each of the cooling holes 30 includes spanwise spaced apart upper and lower hole surfaces 46, 48 along a corresponding adjacent pair of upper and lower ones 25, 26 of the axial partitions 68. A spanwise height H of the hole 30 is defined between the upper and lower hole surfaces 46, 48 of the upper and lower ones 25, 26 of the axial partitions 68 as illustrated in FIG. 3. The metering section 100, the diverging section 102, and the trailing edge cooling slot 66 have downstream extending first, second, and third lengths L1, L2, and L3 respectively as illustrated in FIG. 3.

Referring to FIGS. 3, 5, and 6, aft ends 86 of the partitions 68 have aerodynamically-shaped swept boat tails 88 design and shaped to reduce aerodynamic losses due to flow separation wakes at the aft ends 86. The swept boat tails 88 are also designed to facilitate flow spreading past the slot breakout 58 at the downstream end 69 of the diverging section 102. Each of the swept boat tails 88 include a boat tail trailing edge 90 extending spanwise between the pressure and suction sidewalls 42, 44 and having an apex 92 spanwise located between the breakout lip 49 or the pressure sidewall 42 and the suction sidewall 44 as illustrated in FIG. 6. The boat tail trailing edge 90 sweeps aftwardly or downstream from the apex 92. The boat tail trailing edge 90 sweeps from the apex 92 spanwise or radially outwardly to the breakout lip 49 or the pressure sidewall 42 and inwardly to the suction sidewall 44 from the apex 92. Each of the swept boat tails 88 includes rounded cross sections 96 through the aft ends 86 of the partitions 68 between spanwise pairs 94 of adjacent cooling holes 30. The boat tail trailing edges 90 provide additional strength at the breakout lip 49 and merges the flows of the different cooling holes 30 at the floor or deck 130 upstream of the breakout 58 which is an exit of the cooling holes 30.

The cooling holes 30, the trailing edge cooling slot 66, and the swept boat tails 88 are designed to provide a spanwise deck 130 film effectiveness over the entire slot deck 130 all the way downstream or aft to the terminus of the deck 130 the airfoil trailing edge TE, even at significantly reduced cooling flow. Airfoil cooling design studies have shown a potential cooling flow reduction of about 10 percent of stage 1 blade flow. The study also indicated at the same time, trailing edge temperatures are still 80 to 90 degrees F. lower that more conventional slot designs, so further flow reductions are possible. This is a significant benefit to engine performance.

Referring to FIGS. 3-5, a hole width W of the hole 30 is defined between pressure and suction sidewall surfaces 39, 40 of the pressure and suction sidewalls 42, 44 respectively as illustrated in FIG. 4. The trailing edge cooling slot 66 and the deck 130 are open and exposed to the hot combustion gases 19 that pass through the high pressure turbine 22. The deck 130 extends for the entire third length L3 along the suction sidewall 44.

The adjacent pair of upper and lower ones 25, 26 of the axial partitions 68 and the pressure and suction sidewalls 42, 44 spanwise bound the hole 30. Referring to FIGS. 7 and 8, the cooling hole 30 has a generally spanwise elongated flow cross section 74 and the spanwise height H is substantially greater than the hole width W. The cooling hole 30 has a height to width ratio H/W in a range of about 2:1 to 10:1 (see FIGS. 7-12). The pressure and suction sidewall surfaces 39, 40 of the pressure and suction sidewalls 42, 44 respectively widthwise bound the hole 30.

The embodiment of the cooling hole 30 illustrated in FIG. 4 has a fixed or constant width W through the cooling hole 30 and the pressure and suction sidewall surfaces 39, 40 are parallel through the entire first and second lengths L1, L2 of the cooling hole 30. The pressure sidewall surface 39 is flat or planar through the entire metering and diverging sections 100, 102 and their corresponding first and second lengths L1, L2 of the cooling hole 30. In this embodiment of the cooling hole 30, the suction sidewall surface 40 is flat or planar through the entire metering and diverging sections 100, 102 and their corresponding first and second lengths L1, L2 of the cooling hole 30. The deck 130 is coplanar with suction sidewall surface 40 in the hole 30. The inlet 70, the metering section 100, and the diverging section 102 have the same hole width W or are of constant width W in the embodiment of the trailing edge cooling holes 30 illustrated in FIG. 3 and schematically illustrated in solid line in FIG. 4. The diverging section 102 diverges in a spanwise direction.

The cooling holes 30 and trailing edge cooling slot 66 are cast in cooling features. Casting these features provides good strength, low manufacturing costs, and durability for the airfoil and blades and vanes. The race track shaped flow cross section 74 with the rectangular section 75 between spanwise or radially spaced apart rounded or semi-circular inner and outer end sections 82, 84 provides good cooling flow characteristics which reduces the amount of the coolant flow 52 needed to cool the airfoils. The bottom corner radii RT contribute to good cooling, castability, and strength of these cooling features.

Four exemplary shapes suitable for the flow cross section 74 are illustrated in FIGS. 9-12. The race track shaped flow cross section 74 illustrated in FIG. 9 is spanwise elongated, has four equal corner radii R, and has a width to height ratio W/H in a range of 0.25-0.50. The race track shaped flow cross section 74 illustrated in FIG. 10 is spanwise elongated, has four equal corner radii R, and has a width to height ratio W/H in a range of 0.15-0.50. The race track shaped flow cross section 74 illustrated in FIG. 11 is similar to the one illustrated in FIG. 9 but has unequal top and bottom corner radii RT, RB. An exemplary range of a corner ratio RB/RT is 1-3. The race track shaped flow cross section 74 illustrated in FIG. 12 is spanwise elongated and fully curved and includes curved quarter sides 78 that may be elliptical, parabolic, or polynomial blends.

The spanwise elongated metering section 100 with the constant width W is sized to control the quantity of coolant flow 52 to benefit the engine cycle. The spanwise elongated metering section 100 and diverging section 102 expand the flow coverage at the breakout 58, evenly distributes coolant flow 52 in the trailing edge cooling slot 66. The constant width W metering section 100 upstream of the diverging section 102 of the hole 30 helps keep the coolant flow 52 fully attached in the diverging section 102.

The constant width and separately the planar pressure sidewall surface 39 of the cooling hole 30 helps keep a coolant velocity of the coolant flow 52 and a gas velocity of the hot combustion gases along the external surface 43 of the pressure sidewall 42 at the breakout about equal to minimize aero losses which could result in a negative effect on turbine efficiency. These two features also help keep the coolant flow 52 flow attached in the slot 66.

The present invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. While there have been described herein, what are considered to be preferred and exemplary embodiments of the present invention, other modifications of the invention shall be apparent to those skilled in the art from the teachings herein and, it is, therefore, desired to be secured in the appended claims all such modifications as fall within the true spirit and scope of the invention. 

Accordingly, what is desired to be secured by Letters Patent of the United States is the invention as defined and differentiated in the following claims:
 1. A gas turbine engine turbine airfoil comprising: widthwise spaced apart pressure and suction sidewalls extending outwardly along a span from an airfoil base to an airfoil tip; the pressure and suction sidewalls extending chordwise between opposite leading and trailing edges; a spanwise row of spanwise spaced apart trailing edge cooling holes encased in the pressure sidewall and ending at a single spanwise extending trailing edge cooling slot extending chordally substantially to the trailing edge; each of the cooling holes including in downstream serial cooling flow relationship, a curved inlet, a metering section with a constant area and constant width flow cross section, and a spanwise diverging section leading into the trailing edge cooling slot; axial partitions extending chordally between and radially separating the cooling holes along the span; and aft ends of the partitions including swept boat tails.
 2. The airfoil as claimed in claim 1 further comprising a spanwise heights substantially greater than hole widths through the cooling holes.
 3. The airfoil as claimed in claim 1 further comprising pressure and suction sidewall surfaces of the pressure and suction sidewalls respectively in the hole and the pressure sidewall surface being planar through the entire metering and diverging sections.
 4. The airfoil as claimed in claim 3 further comprising the width being constant through the metering and diverging sections of the hole.
 5. The airfoil as claimed in claim 1 further comprising: a deck in the slot extending chordwise or downstream from the diverging sections of the cooling holes substantially to the airfoil trailing edge, the deck extending spanwise or radially outwardly from a bottommost one to a topmost one of the trailing edge cooling holes, upper and lower deck sidewalls spanwise bounding the deck and extending from the deck to an external surface of the pressure sidewall, and fillets in slot corners between the upper and lower deck sidewalls and the deck.
 6. The airfoil as claimed in claim 5 further comprising the fillets having fillet radii substantially the same size as bottom corner radii of the flow cross section of the diverging sections adjacent the bottom corner radii.
 7. The airfoil as claimed in claim 4 further comprising: the diverging section having a race track shaped flow cross section, the race track shaped flow cross section including a rectangular section between spanwise spaced apart rounded or semi-circular inner and outer end sections having radii, a deck in the slot extending chordwise or downstream from the diverging sections of the cooling holes substantially to the airfoil trailing edge, the deck extending spanwise or radially outwardly from a bottommost one to a topmost one of the trailing edge cooling holes, upper and lower deck sidewalls spanwise bounding the deck and extending from the deck to an external surface of the pressure sidewall, fillets in slot corners between the upper and lower deck sidewalls and the deck, and the fillets having fillet radii substantially the same size as the radii of the flow cross section.
 8. The airfoil as claimed in claim 1 further comprising: the boat tails being swept, each of the boat tails including a boat tail trailing edge having an apex spanwise located between the pressure and suction sidewalls, the boat tail trailing edge sweeping aftwardly or downstream from the apex, and the boat tail trailing edge sweeping from the apex spanwise or radially outwardly to the pressure sidewall and inwardly to the suction sidewall from the apex.
 9. The airfoil as claimed in claim 8 further comprising the swept boat tails including rounded cross sections through the aft ends of the partitions between spanwise pairs of adjacent cooling holes.
 10. The airfoil as claimed in claim 9 further comprising the metering and diverging sections having a hole height to hole width ratio of the spanwise height and the hole width in a range of about 2:1 to 10:1.
 11. The airfoil as claimed in claim 9 further comprising pressure and suction sidewall surfaces of the pressure and suction sidewalls respectively in the hole and the pressure sidewall surface being planar through the entire metering and diverging sections.
 12. The airfoil as claimed in claim 11 further comprising the width being constant through the metering and diverging sections of the hole.
 13. The airfoil as claimed in claim 12 further comprising the inlet being downstream converging or bellmouth shaped.
 14. A gas turbine engine turbine airfoil comprising: widthwise spaced apart pressure and suction sidewalls extending outwardly along a span from an airfoil base to an airfoil tip; the pressure and suction sidewalls extending chordwise between opposite leading and trailing edges; a spanwise row of spanwise spaced apart trailing edge cooling holes encased in the pressure sidewall and ending at a single spanwise extending trailing edge cooling slot extending chordally substantially to the trailing edge; each of the cooling holes including in downstream serial cooling flow relationship, a curved inlet, a metering section, and a spanwise diverging section leading into the trailing edge cooling slot; axial partitions extending chordally between and radially separating the cooling holes along the span; and aft ends of the partitions including swept boat tails.
 15. The airfoil as claimed in claim 14 further comprising: the boat tails being swept, each of the boat tails including a boat tail trailing edge having an apex spanwise located between the pressure and suction sidewalls, the boat tail trailing edge sweeping aftwardly or downstream from the apex, and the boat tail trailing edge sweeping from the apex spanwise or radially outwardly to the pressure sidewall and inwardly to the suction sidewall from the apex.
 16. The airfoil as claimed in claim 15 further comprising the swept boat tails including rounded cross sections through the aft ends of the partitions between spanwise pairs of adjacent cooling holes.
 17. The airfoil as claimed in claim 16 further comprising: a deck in the slot extending chordwise or downstream from the diverging sections of the cooling holes substantially to the airfoil trailing edge, the deck extending spanwise or radially outwardly from a bottommost one to a topmost one of the trailing edge cooling holes, upper and lower deck sidewalls spanwise bounding the deck and extending from the deck to an external surface of the pressure sidewall, and fillets in slot corners between the upper and lower deck sidewalls and the deck.
 18. The airfoil as claimed in claim 17 further comprising the fillets having fillet radii substantially the same size as bottom corner radii of the flow cross section of the diverging sections adjacent the bottom corner radii.
 19. The airfoil as claimed in claim 16 further comprising: the diverging section having a race track shaped flow cross section, the race track shaped flow cross section including a rectangular section between spanwise spaced apart rounded or semi-circular inner and outer end sections having radii, a deck in the slot extending chordwise or downstream from the diverging sections of the cooling holes substantially to the airfoil trailing edge, the deck extending spanwise or radially outwardly from a bottommost one to a topmost one of the trailing edge cooling holes, upper and lower deck sidewalls spanwise bounding the deck and extending from the deck to an external surface of the pressure sidewall, fillets in slot corners between the upper and lower deck sidewalls and the deck, and the fillets having fillet radii substantially the same size as the radii of the flow cross section.
 20. The airfoil as claimed in claim 19 further comprising the metering and diverging sections having a hole height to hole width ratio of the spanwise height and the hole width in a range of about 2:1 to 10:1. 